What do you mean by worst case?

As you said these sites are likely to overrepresent waitlisted people. As a fellow waitlisted person, I'm using them to get an idea of how "bad" the situation is, i.e. to curb my expectations about moving to the reservation list at some point. Waitlisted people being overrepresented will make the situation look worse than it is, meaning I'm more likely to be positively surprised than negatively.